Bump graphene-django from 2.3.2 to 2.4.0 in /backend
Bump graphene-django from 2.3.2 to 2.4.0 in /backend

Bumps [graphene-django](https://github.com/graphql-python/graphene-django) from 2.3.2 to 2.4.0.
- [Release notes](https://github.com/graphql-python/graphene-django/releases)
- [Commits](https://github.com/graphql-python/graphene-django/compare/v2.3.2...v2.4.0)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
patrick91/pycon,patrick91/pycon